John Cappa
Former Editor, Four Wheeler
Most everyone agrees that the ’07-’11 Jeep Wrangler is pathetically underpowered. The 3.8L’s 205hp may sound like a lot on paper, but when you consider that many lifted and well-armored JKs tip the scales into 5,000, 6,000, and even 7,000 pounds, you realize it’s basically the same weight as a modern-day ¾- or 1-ton truck, only with a V-6. When was the last time you drove a 1-ton dualie with a V-6?
Of course, adding headers, exhaust, chip, air filter, and so on can provide a minor, although a mostly unnoticeable power improvement. The truth of the matter is that the only way to really make any significant power from the 3.8L is to swap it out for a V-8 or add boost.
Our ’07 Wrangler Unlimited Rubicon features a factory six-speed manual transmission, 37-inch tires, a Dynatrac ProRock 60 rear axle, 5.13 gears, and is heavy, but relatively lightweight compared to some of the porky, up-armored JKs out there. After spending several slow-speed years behind the wheel, it was time to step it up a notch. We decided against a motor swap for many reasons. A motor swap in a JK can be an expensive proposition and it often leads to other necessary modifications like transmission and axle upgrades. Adding a supercharger to the factory 3.8L is significantly less expensive and less detrimental to the factory drivetrain parts. Think of it as the equivalent of installing a small V-8 without the hassle of messing with adapters, the motor mounts, the exhaust, the cooling system, the driveshafts, and so on. Dollar for dollar, nothing makes more useable bolt-on horsepower and torque than a supercharger. We went with a Magnuson intercooled supercharger because of the company’s attention to detail and experience with supercharging everything from a Jeep 3.8L V-6 to a fire-breathing Corvette Z06 7.0L LS7.
The Install
The Magnuson Jeep 3.8L supercharger kit includes a Sixth Generation Eaton MP1320 TVS supercharger with integral-bypass valve and intake manifold, high-flow fuel injectors, liquid-to-air intercooler, Diablo Sport Trinity handheld programmer, large front-mounted heat exchanger, all the necessary fittings, lines, belts, and hardware required, a standard three-year/36,000-mile warranty on the supercharger hardware, and a one-year limited warranty on electronics. The kit is 50-state legal on ’07-’10 Wranglers. It’s 100-percent bolt-on and fits under the factory hood. The kit takes 8 to 10 hours to install and can be done at home, however it’s a good idea to take it to a qualified shop or have someone on-hand that has made this kind of engine modification before. You can download and read over the detailed 167-step installation manual online to see if you are up to the task.
1. We like that the supercharger kit retains the factory airbox. It’s true that the factory airbox will limit airflow at higher rpms, however it keeps dirt and water out of the engine better than an aftermarket open-air element. Note the relocation of the battery. It’s now turned 90 degrees. Aftermarket dual battery kits will likely need to be scrapped to fit the supercharger.
2. The Eaton TVS1320 Hybrid-roots supercharger is a sealed unit with its own oil supply. It can go 80,000 to 120,000 miles between oil changes.
3. The 3.8L V-6 oil fill is already a little difficult to access from the factory and typically requires a funnel to add oil without making a mess. Adding the supercharger and new Magnuson intake makes a long transmission funnel almost mandatory for adding oil. Magnuson told us there is a bolt-on oil-fill extension in the works.
4. The liquid-to-air heat exchanger fits in front of the radiator. Unfortunately, it decreases the efficiency of the already anemic 3.8L A/C system. The heat exchanger is fed via a small electric water pump and reservoir that fits under the hood, which circulates the fluid to the supercharger and back.
On-Road
What you will notice first is the improved and incredibly flat power curve provided by the addition of the Magnuson supercharger. The 3.8L is actually more civilized with the supercharger because you can lug the engine at low rpms where it would previously stall. For example, starting out in Second gear from a dead stop is easy, whereas the stock 3.8L would have fallen flat on its face. We can pull very steep grades in Sixth gear at about quarter throttle. The bad news is that our supercharged 3.8L requires 91-octane fuel. We can muster about 12 mpg on the highway and about 9-10 mpg around town.
It’s not all gumdrops and puppies, though—the included heat exchanger blocks the radiator area. The engine still runs plenty cool, but the already-anemic early-JK A/C system now almost never produces cold air, unless it’s cold outside. Also, the oil fill on the 3.8L has never been all that easy to get to. With the new Magnuson intake and supercharger in place it’s nearly hidden, and for sure requires a long funnel, but Magnuson is said to be working on a bolt-on extension.
Thus far our supercharged Jeep has only had one episode. The check engine light came on while wheeling at 4,000 to 6,000 feet of elevation. It ran fine with the light on, though. We drove it 40 miles home with the light on. At about the last 5-10 miles, a red lightning bolt on the dash started flashing and the engine started missing very badly. We limped it home, checked around under the hood and found nothing wrong. After the Jeep sat a while, we restarted the engine and the check engine light went out as did the flashing red lightning bolt. The engine ran fine again. We called Magnuson about the issue and were told to connect the included programmer to read the codes if it happened again. We have not been able to replicate the issue during the 1,400-mile on- and off-road testing.
We called a friend who has messed with superchargers on 3.8L V-6 Jeep engines to get some insight. He believes it’s one of the sensors getting upset over the 5 psi of boost. He has seen this same issue with other superchargers on the 3.8L. He says it goes away when you cycle the key a couple times. That would explain our Jeep resetting itself.
Off-Road
If you frequent off-road spots with mud or sand that require high-range 4WD and a little wheelspeed, you will absolutely love the addition of a Magnuson supercharger. Before adding boost, our low-geared Rubicon transfer case made the Jeep unbearable. Low range was too low to produce any real wheelspeed and high range 4x4 was too much for the poor 3.8L to even think about spinning any other gear but First. With the supercharger, we can now lug Second gear in the dunes and even up-shift to Third if need be. Off-road fuel economy averages to about 10 mpg. Chugging along over boulders is also made easier with the supercharger thanks to the increased torque. More off-idle torque allows the 3.8L Jeep to burble along over boulders with little to no throttle input.
Bottom Line
The Magnuson supercharger kit is a relatively simple, smog-legal, bolt-on upgrade that offers a huge improvement in power both on- and off-road. It’s a lot less expensive than a Hemi swap, but it’s no replacement for a V-8 if that’s the kind of raw, unbridled power and torque you crave. Contrary to what some people believe about superchargers, our fuel economy suffered significantly. We lost anywhere from 2-5 mpg overall, depending on driving conditions. Don’t forget that you have to run more expensive 91-octane, too.
